1. Field of the Invention
This invention relates to a resistance change memory device, which stores a resistance value determinable by a resistance change of memory material in a non-volatile manner.
2. Description of the Related Art
Recently, there have been proposed some memory devices having variable resistance elements. One of such the memory devices is known as a phase change memory which uses phase transition between an amorphous state and a crystalline state of a memory material (for example, U.S. Pat. No. 6,314,014B1).
In such the phase change memory device, by controlling the current of a chalcogenide cell, reversible switching may be performed between a crystalline state (i.e. low resistance state) and an amorphous state (i.e. high resistance state).
Apply a large current to a cell so as to cause the cell chalcogenide to be melted, then rapidly cool down it, and a low resistance state may be written. Anneal the chalcogenide in such a degree as to crystallize it without melting, and a high resistance state may be written. Therefore, it is possible to obtain an electrically rewritable non-volatile memory device.
Other programmable resistance memories have been proposed as including programmable resistances switchable between a low resistance state and a high resistance state by reversing the polarity of voltage application. One of these has an ion conductor formed of a chalcogenide containing metals (for example, U.S. Pat. No. 6,418,049B1), and another one has a polymer in which conductive particles are dispersed (for example, U.S. Pat. No. 6,072,716).
In these memories, dendrite growth and retraction thereof in a solid by voltage application are used. In order to write a low resistance state into a cell, a voltage is applied between the anode and cathode of a cell in such a polarity that the anode is positive. As a result, a dendrite grows from the cathode to reach the anode, whereby the cell becomes to be a low resistance state. A reverse voltage application retracts the dendrite to cause the cell to be in a high resistance state. Such the resistance change is reversible, and the low resistance state and the high resistance state may be stored in a non-volatile manner.
It has been suggested that it is possible to achieve an electrically rewritable non-volatile memory with a high density by use of such the programmable resistance. However, there has not been proposed a detailed configuration of a cell array and a read/write circuit thereof.
In order to achieve a practical non-volatile memory with a high density and a high performance, how to combine the programmable resistance with what kinds of switching devices for constituting a cell array, how to construct the read/write circuit in communication with the cell array, and the like become important technical issues.